The invention relates to a method for starting a power plant having at least one turbo group and one recuperator
A power plant conventionally comprises a turbogroup with at least one turbine and with at least one main combustion chamber which is assigned at least one burner and which is arranged upstream of the turbine and, during operation, generates hot gases acting upon the turbine. A generator for current generation may be drive-connected to this turbogroup. With the aid of a recuperator, which is arranged, on the one hand, in a first flow path leading exhaust gas away from the turbogroup and, on the other hand, in a second flow path leading fresh gas toward the turbogroup, heat is extracted from the exhaust gases during normal operation, in order thereby to preheat the fresh gases. Moreover, to increase efficiency, an additional firing device, by means of which the temperature level of the preheated fresh gases supplied to the turbogroup can be additionally increased, may be arranged within the recuperator in the first flow path leading the exhaust gases.
The power plant can be shut down during times of low current demand, for example at night or at the weekend, or for maintenance purposes. As a result, in particular, the turbogroup and the recuperator cool down to a greater or lesser extent. In this case, as a rule, the recuperator cools down more rapidly than the components of the turbogroup. So that the power plant or the respective turbogroup can develop its full power output as quickly as possible, it is expedient, for starting the plant, to preheat the recuperator. Particularly with regard to gas storage power plants within what is known as a Compressed-Air Energy Storage System, CAES system in short, starting operations occur relatively frequently. This is because the basic idea of a CAES system is seen in storing excess energy generated by permanently operated power plants during the base-load times and utilizing it later, for example, for peak-load generation. This is achieved in that air or another gas is pumped under relatively high pressure with the aid of the excess energy into a store, from which the air or the gas can be extracted, as required, for current generation. This means that the energy is kept retrievably in stock in the form of potential energy. Used-up coal mines or salt mines, for example, serve as stores.
For the profitability of power plants, in particular of gas storage power plants, therefore, it is of considerable usefulness to shorten the starting procedure.
An important measure for shortening the starting procedure is seen in the preheating of the recuperator. In this case, it is basically possible to preheat the recuperator by putting into operation the additional firing device normally arranged in the recuperator. However, this may give rise locally in the recuperator, in particular near the additional firing device, to hot zones or spots, the temperature of which is above a self-ignition temperature of a fuel/oxidizer mixture which is supplied to the main combustion chamber for combustion in order to start the turbogroup. Hot zones or spots of this kind have a disadvantage when, with the recuperator preheated, an attempt to ignite the main combustion chamber goes wrong, since the combustible fuel/oxidizer mixture then comes into contact with these hot zones or spots and may ignite there in an undesirable way.
The invention is intended to remedy this. The invention, as characterized in the claims, is concerned with the problem, for a power plant with a turbogroup and a recuperator, of finding a way of making it possible to have a shortened starting method during which the recuperator is preheated, without the risk of critical local hotspots at the same time occurring in the recuperator.
This problem is solved by means of the subject of the independent claims. Advantageous refinements are the subject matter of the dependent claims.
The present invention is based on the general idea of preheating the recuperator with the aid of an auxiliary combustion chamber which is assigned at least one burner and which is arranged outside the first flow path, that is to say, in particular, outside the recuperator. This measure makes it possible to ensure in a particularly simple way that the critical self-ignition temperature of the fuel/oxidizer mixture is not reached at any point in the first and/or in the second flow path and therefore in the recuperator. The invention thus makes it possible, should an attempt to ignite the main combustion chamber fail, to reduce or avoid the risk of undesirable self-ignition of the fuel/oxidizer mixture in the system as a whole.
Since the auxiliary combustion chamber used for preheating the recuperator is arranged outside the first flow path, the temperature in the first flow path or in the recuperator cannot at any point be higher than that temperature which the gas generated by the auxiliary combustion chamber and fed into the first flow path possesses, this temperature being relatively easily controllable. In particular, in the case of this externally arranged auxiliary combustion chamber, it is unimportant whether the critical self-ignition temperature is exceeded or not locally in it, since the external auxiliary combustion chamber cannot come into contact with the explosive fuel/oxidizer mixture even in the case of a misignition of the main combustion chamber. It may even be expedient, with the aid of the additional firing device, first to generate fuel gases, the temperature of which is above the critical self-ignition temperature, appropriate quantities of cold gases being admixed before the feed into the first flow path, in order to lower the temperature of the gas mixture ultimately supplied to the first flow path below the critical self-ignition temperature. This admixing of cold gas preferably takes place even within the auxiliary combustion chamber, for example by means of a corresponding secondary gas supply.
According to a preferred embodiment, during the preheating of the recuperator, the second flow path may be acted upon by a fresh gas flow flowing through the recuperator, in such a way that a predetermined temperature distribution is formed in the recuperator. This procedure makes it possible to set at the recuperator a temperature distribution which corresponds essentially to that temperature distribution which is established in the recuperator after the start of the turbogroup when the power plant is operating under nominal conditions. This measure thus prevents damage to components of the recuperator as a result of thermal load errors.
In an expedient refinement, this fresh gas flow may be extracted from the second flow path downstream of the recuperator and introduced into the first flow path, upstream of the recuperator, via a first bypass line bypassing the turbogroup. The recuperator can be heated independently of the turbogroup by means of this measure.
An embodiment in which a fresh gas flow used for acting upon the recuperator is employed for purging the turbogroup is particularly advantageous. By virtue of this measure, on the one hand, the turbogroup, too, can be preheated, since the fresh gas flow supplied is preheated in the recuperator. On the other hand, permanent purging of the turbogroup, in particular the main combustion chamber, also takes place as a result, so that even here, before the ignition operation, a separate purging operation can be dispensed with.
According to a particularly advantageous embodiment, the power plant may be designed as a gas storage power plant with a gas store, the fresh gas flow used for acting upon the recuperator and/or for purging the additional firing device and/or for purging the turbogroup, in particular the main combustion chamber, is generated by the extraction of fresh gas from the gas store. Thus, by means of this procedure, the energy stored in any case is used for generating the necessary fresh gas flow, so that additional components for providing the gas are dispensed with.
Since, according to an expedient embodiment, the auxiliary combustion chamber is run down to operation under minimum conditions before the ignition of the main combustion chamber, the preheating of the recuperator and, in particular, of the entire gas-leading system can be maintained even in the event of a misignition of the main combustion chamber. Time delays and energy losses due to a misignition of the main combustion chamber can thereby be reduced.
Further important features and advantages of the invention may be gathered from the subclaims, from the drawings and from the accompanying figure description with reference to the drawing.